First Start up - and Running Rich

[AGrinthal]

I have just got my cub going after a total rebuild on engine. She starts fine and seems to idle pretty well. I have run it for less than 30 minutes and haven't moved it since I have the hood off and I'm using a gas drip bottle tied to a post. Here's my question. I took the plugs out to do a compression test and they are black (compression was ok.. about 109 across the board... up from 60 when tested without it having run. I would think that figure would get better as the rings seat).

Also it seemed to me it was eating a lot of gas for just sitting there idling. after do some research I see there isn't much to do to change the Mixture. The carb has been rebuilt and I did spend a lot of time on the float adjustment. I read somewhere that a cub idles rich since the jets are fixed and meant to be under load. So I guess what I'm asking is once I take it for a spin and put some loading on it.. I should see cleaner plugs?

Like I said it starts right up and idles pretty smoothly.. Just don't like the black plugs and what seems like a healthy gas drinker..

Andy
Andover, NJ

[havoc1482]

How does it act with different choke positions?

[Eugene]

Don't get excited about the soot on the spark plugs at this time. As long as the engine starts easily and runs reasonably well - leave things alone for a while.

Fuel consumption. As long as you are not dripping gas out of the carburetor - leave things alone for a while. Fuel consumption at low idle will be some where around 1/4 to 1/3 gallon per hour. High idle and under heavy load the engine will consume about 1 gallon per hour.

Let the engine warm up, get broken in, then you can make some final adjustments.

The Operator's Manual has a section titled "Tractor Break-in Period". It takes at least 25 hours (clock hours) to break in a rebuilt engine.

[Rick Spivey]

Agree with Eugene, however, there is a mixture adjustment on top of the carb. It adjusts the air, not gas, so opening it outward would lean out the mixture. I usually start at 1.5 turns out from the seated position, then adjust, looking for two things:
- no black smoke at idle
- a smooth ramp-up to fast idle (no stumbling or hesitation, and minimal or no black smoke)
It wouldn't hurt to check that mixture screw.

[AGrinthal]

I'm revisiting this thread. I have used my cub now for many hours over the summer to plow fields (sad it got dirty!) and this winter I have the grader blade set up in front as a snow plow. (made my front gear box leak a little) So she's been getting plenty of use. I'm back though on my running rich soap box. I have black soot on my hood after running it for a while (which of course I wipe off and re-wax).

She starts fine and runs fine but I have the above observation and the following. I NEVER have to choke it. In fact I didn't even put the choke pull back on. This winter even in VERY cold conditions she starts right up. NO choke. I've had two days where the temp may have been single digit and she starts right up but stumbles for a second or two. But after that she's fine.

I'm an anal Mech Engineer and she really runs fine EXCEPT for the soot issue. I'm sure if I take the plugs out they will be black. I don't think gas consumption is bad and like I said I have quite a few hours of plowing and discing on it and she runs strong. I just want it run the way it should.. There shouldn't be black soot on the hood after running 15 minutes. Eventually that all buildsup.

Just wondering what to do..
Thanks
Andy



PS The carb was completely refurbished. Even had the top milled flat. And the guy who did it said it has THE CORRECT jet fitted for the serial number.

[Papa's Cub]

Well, the first thing I would do is to repair the exhaust leak. Since this allows soot to accumulate on the hood it would at least remedy that problem. Sounds as if you have it tuned to perfection. Just a thought, out of sight...out of mind!
Good Luck, Tom.

[gitractorman]

What plugs are you running. Yes, Cubs tend to run quite rich in my opinion and there's little adjustment in the carb for this. If you are running the D-16 plugs, change up to D-21, the hotter plugs will definitely burn a bit cleaner. Starting without choke sounds to me like it's tuned just about perfect. Mine ran that way after I had been through them, and I rarely ever had to choke a Cub to get it started, even on the coldest days.

[Rick Spivey]

I'm not doubting the guy who rebuilt the carb. But my son's cub had the same rich issue, with soot on my garage door and his hood. A new carb finally solved it, the old one simply wouldn't be rebuilt correctly. I never figured out why, and I am not a guy who gives up easy. At any rate, try and locate a smaller main jet , and give it a spin. Ours had been drilled out, but even when replaced, we couldn't get it right. Some carbs may just never run right, possibly a mix of parts, ?????? Couldn't hurt to try, you should probably be able to tell if it goes too lean (under a load).